Method and Apparatus for Extracting Frozen Volatiles from Subsurface Regolith

ABSTRACT

A volatile extraction well and method to utilize heat, which could be from the sun or from some other energy source, to directly vaporize subsurface water-ice, or other frozen volatile substance, in-situ. The pressure of the vaporized water (or other volatile gas) released in the heated soil causes the vapor to flow into a sealed drill-hole, or well, and on through an extraction tube to a surface collection vessel where it is condensed and stored.

FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT

This invention was made with Government support under contract NNX12CD91P awarded by NASA. The Government has certain rights in this invention.

FIELD OF THE INVENTION

The present invention relates generally to extraction of chemical vapors from soils, and more particularly to the use of heat to extract frozen volatile chemicals, such as water vapor, from sub-surface frost deposits in soils, terrestrially or on other solar-system bodies.

BACKGROUND OF THE INVENTION

It has long been known that large quantities of water ice exist in extraterrestrial solar system bodies such as comets and the moons of various planets; however, ever since the Lunar Prospector mission in 1998 indicated that significant quantities of ice likely exist in subsurface deposits on the earth's moon (in shadowed craters) there has been increased interest in that resource. More recent space missions have confirmed the existence of large quantities of subsurface ice on the Earth's moon. That knowledge, as well as confirmation that ice is present in many Near-Earth-Objects (NEOs) and asteroids, and on Mars, has increased interest in methods to extract and utilize that resource. The most commonly discussed methods of utilizing components of regolith (including volatiles) involve mining or extracting the regolith, transporting it to a processing unit, and then adding heat or using other means to extract the components of interest in a fixed, sealed processing unit. (Regolith is a region of soil-like loose unconsolidated rock and dust that overlies bedrock on the Earth, Moon or other solar-system body.) One recent proposal for extracting lunar (or Martian) ice [Zacny, K., G. Paulsen, J. Craft, L. Oryshchyn, J. Sanders, R. Mueller (2012) “Mars In-Situ Water Extractor (MISWE),” in: Concepts and Approaches for Mars Exploration, held Jun. 12-14, 2012 in Houston, Tex. LPI Contribution No. 1679, ID.4268] suggested mounting a processing unit on a mobile rover so that extracted regolith would not need to be transported to a fixed processing location, but could be processed near where it was mined (and after the water was removed, the waste material could be left on the surface nearby)—saving the cost and effort of transporting the regolith. Terrestrially fossil energy resources that are solids, or cannot be easily separated from solids (such as coal, bitumin in tar-sands, or kerogen in oil-shale) are usually recovered by mining and post-processing. Terrestrial fossil-energy resources which can be extracted in the form of fluids (i.e., liquids or gases such as oil or natural gas) are typically removed from the surrounding rock in situ, and only the fossil-fuel is processed or refined as needed (i.e., the rock is left in place, except for the well bore).

Lunar soil has a very low thermal conductivity under insitu vacuum conditions, typically on the order of 0.00015 W/cm K. If an intersitital gas, at a pressure approaching atmospheric pressure on earth, is introduced into the regolith, then the effective thermal conductivity of lunar regolith increases by as much as a factor of 100 over its value under vacuum conditions. Twenty years ago Wittenberg [Wittenberg, L J (1993) “In-situ Extraction of Lunar Soil Volatiles” WCSAR-TR-AR3-9311-3, Univ. Wisconsin, Madison, Wis.] proposed taking advantage of such an increase in effective thermal conductivity when an interstitial gas is present to facilitate extraction of Helium gas (containing high concentrations of the isotope Helium-3) from lunar regolith. Wittenberg proposed heating a region of near-surface lunar regolith, covered with an impermeable dome and pressurized with hydrogen gas, as a means of extracting and collecting Helium gas containing the Helium-3 released from the heated regolith. The method and approach for heating the regolith suggested by Wittenberg (e.g., heat pipes) could also function for extracting water vapor or other frozen volatile substances from near-surface regolith; however, the approach requires significant infrastructure and would be complex to operate. Clearly more efficient means of extracting gases from sub-surface deposits containing these volatile substances in frozen solid form would be very beneficial and could enable efficient utilization of those resources. The present invention offers significant benefits over methods currently proposed for extracting frozen volatile substances from sub-surface deposits on airless solar-system bodies. The present invention would require less work, less infrastructure and would be more efficient than the alternative methods proposed by Zacny or Wittenberg.

SUMMARY OF THE INVENTION

The invention is a method and apparatus to utilize heat, which could be from the sun or from some other energy source, to directly vaporize subsurface water-ice, or other frozen volatile substance, in-situ. The pressure of the vaporized water (or other volatile gas) released in the heated soil causes the vapor to flow into a sealed drill-hole, or well, and on through an extraction tube to a surface collection vessel where it is condensed and stored.

In its simplest form the volatile extraction well will function without down hole pumps, compressors or other gas-moving equipment, relying instead on thermal radiation and thermal conduction to transfer heat from a heat-source in the well to the surrounding subsurface regolith, and subsequent increased vapor pressure of the released gas to induce it to flow to the collection location(s). In one embodiment an extraction ‘well’ for frozen volatiles in low-permeability regolith deposits on the moon, Mars or other extraterrestrial body, can consist of a straight (vertical or inclined) drill hole, or ‘well’, into the subsurface region of regolith which contains the desired frozen components. Alternative configurations, which can target a volatile-rich layer, can be constructed utilizing curved or ‘flexible’ drilling and conveying methods. By using curved or horizontal drill holes a single entrance hole could be utilized to extract volatiles from wide ranging sub-surface volatile deposits, at lateral distances of up to many 10's of meters from the entrance hole. Yet another embodiment of the invention achieves enhancement to lateral permeability for transport of volatiles by drilling several adjacent horizontal sub-surface holes and then carefully, and in a controlled manner, over-pressurizing them (sequentially, in targeted sections) to temporarily lift the overburden, just slightly—creating a high permeability horizontal region between adjacent horizontal wells, in a manner somewhat analogous to hydraulic fracturing for terrestrial natural-gas wells, but utilizing a gas instead of a liquid to produce a new dilated high-permeability horizontal-layer in the regolith.

An aspect of the invention is a volatile extraction well for extracting a frozen subsurface volatile substance from soil or regolith, including a borehole drilled into the soil or regolith; a heating element inserted in the borehole at a depth where the volatile substance is to be extracted and capable of radiating or conducting sufficient thermal energy to the soil or regolith to vaporize the frozen volatile substance; a gas seal formed at or near the top of the borehole to prevent uncontrolled escape of vapor from the borehole when released by the heating element; and an extraction tube or conduit extending through the gas seal for removing vapor from the borehole when released by the heating element. Another aspect of the invention is a method for extracting a frozen subsurface volatile substance from soil or regolith, by drilling a borehole into the soil or regolith; inserting a heating element in the borehole at a depth where the volatile substance is to be extracted, the heating element being capable of radiating or conducting sufficient thermal energy to the soil or regolith to vaporize the frozen volatile substance; forming a gas seal at or near the top of the borehole to prevent uncontrolled escape of vapor from the borehole when released by the heating element; and providing an extraction tube or conduit extending through the gas seal for removing vapor from the borehole when released by the heating element. The boreholes may be vertical or tilted at an angle to the vertical or may be curved, and the curved boreholes may have a plurality of substantially horizontal boreholes extending from the bottom of the curved borehole. The heating element may be self-contained or may be connected to a surface mounted energy source, e.g. a solar powered source. A collector and condensor may be connected to the extraction tube or conduit to collect and condense vapor from the borehole, and may maintain the borehole pressure sufficiently low to allow the vapor to flow to the collector and condensor, e.g. at below the boiling pressure of the volatile substance being recovered, corresponding with the temperature of the heated subsurface region of the well.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more fully understood by reference to the following drawings which are for illustrative purposes only:

FIG. 1 is a schematic diagram of a vertical volatile extraction well of the invention showing key components such as a selfcontained subsurface heat source, a vapor-seal near the surface and a vapor collection tube passing through that seal.

FIG. 2 is a schematic diagram of a vertical volatile extraction well of the invention utilizing a means to send energy from a solar collector to a down-hole heating element which heats the surrounding soil, vaporizing the subsurface volatile resource.

FIG. 3 is a schematic diagram of a volatile extraction well of the invention utilizing a curved drill-hole to extract volatiles from locations not directly under the drill hole site.

FIG. 4 is a schematic diagram of a volatile extraction well of the invention utilizing multiple parallel, nearly-horizontal, sub-surface drill-holes, in near proximity to each other, for extraction of volatiles from a distributed region not necessarily directly under the drill hole site

DETAILED DESCRIPTION OF THE INVENTION

Referring more specifically to the drawings, for illustrative purposes the present invention is embodied in the apparatus and method generally shown in FIG. 1 through FIG. 4. It will be appreciated that the apparatus may vary as to configuration and as to details of the parts, and the method may vary as to its particular implementation and as to specific steps and sequence, without departing from the basic concepts as disclosed herein.

The volatile extraction well apparatus and method of the invention utilizes heat radiated and conducted from a subsurface heating element to vaporize the frozen subsurface volatile substance in the surrounding soil or regolith, and utilizes the naturally occurring vapor-pressure of the heated volatile to drive that vapor into the sealed well-hole and through a pipe or tube to a surface-mounted condenser/collector which condenses the volatile vapor and maintains a low pressure in the collection tube and well-hole. On airless bodies such as the moon, or moons of other planets, or asteroids, the method and apparatus can be utilized for extracting volatiles from low-permeability materials such as rocks, soils, or regolith, from subsurface depths which are sufficient to maintain pressures within the well-hole sufficient to drive the vapor to the collection point. For bodies with an atmosphere, such as on Earth or Mars, the pressure in the bore-hole can be maintained at a value lower that the ambient atmospheric pressure (through active or passive control systems, for instance, in the operation of the collector/condenser) so that ambient atmospheric-pressure gas in the pores of the soil or rock can assist in driving the released volatile vapor to the bore-hole and to the collector.

The invention is a method and apparatus to extract a frozen volatile substance, which is distributed throughout a subsurface region, without mining or removing the containing soil or regolith. The method and apparatus utilizes supplied heat to vaporize the volatile substance of interest and then, by maintaining a lower pressure in the well hole than the vapor pressure of the vaporized substance, induces the vapor to migrate to the bore hole where it is extracted through a tube to a collection condensation unit located on the surface. As illustrated in FIG. 1 the supplied heat could be located in a self-contained heating element lowered into the well before it is sealed, which could be be a radioactive source, a chemical heat source or any other self-contained source of energy that will radiate or conduct heat to the surroundings without any subsequent communication or transfer of energy from the surface, except perhaps occasional replacement of the heat source if becomes depleted.

The only drilling required for establishing the collection/recovery system of the invention is a well-bore drill hole, through which the heater and vapor-extraction tube are inserted to a desired depth. After the heater and extraction tube are in place the drill hole, or well, is sealed around the extraction tube, near the entrance, to prevent vapor from leaking out of the vapor extraction well (e.g., with an inflatable bladder, grout, or other means to prevent the loss of volatile gas from the well). As heat is introduced at the desired depth, it is transported by conduction and radiation into the surrounding soil, and the applied heat vaporizes the frozen volatiles, raising the vapor pressure in the interstitial voids within the heated regolith and also in the well-hole, and this over-pressure drives the vapor out through the heated soil to the drill hole and finally out of the well, without the need of any down-hole pumps or compressors, although some embodiments of the invention may utilize mechanically created increases or decreases in pressure in the well or the collector, to increase the flow rate or production rate of the well.

As long as the extraction-well pressure remains below the triple point pressure of the volatile substance being recovered, the simple approach described in the preceeding paragraphs will generally be sufficient. The triple-point pressure for water, however, is only 611 Pa (or 0.6 mbar), and while maintaining the well at such low pressures will facilitate containment of the vapor inside the ‘lid’ formed by the overlying low-permeable regolith covering the volatile extraction region, keeping pressures that low might also limit the overall gas-production-rate obtainable from the well. In order to achieve higher production rates, alternate operating conditions could be utilized. For example, if the temperature were raised above the triple point, then the pressure could still be kept low enough for the heated volatile substance to be above the corresponding boiling temperature, and thus remain in a vapor state, and be easily transported out through the extraction tube in that vapor state. The volatile substance would not condense to form a liquid as long as the temperature were maintained at an appropriately high level throughout the entire vapor collection flow system. For example, for water at pressures below 100 mbar and temperatures above 325 K the water will remain in a vapor state. Operating at temperatures above 325 K would allow pressures to be two orders of magnitude higher than the triple-point of water (e.g., ˜100 mbar instead of less than 0.6 mbar) and still avoid any condensation of liquid water. This higher operating pressure (i.e., up to 100 mbar) would increase the effective thermal conductivity in the regolith/soil as well as increasing the flow rate of the vapor through the regolith, and thus would increase the potential production rate for the extraction of volatiles, over values obtainable if well pressures were maintained below the triple point of water.

Robustness of operation depends on preventing ice-deposits from forming and blocking flow in locations where they could not easily be melted and/or vaporized to restore the system to operating condition. Auxiliary heaters could be utilized along the collection tubes to ensure that the temperature remains high enough to prevent condensation or freezing in the vapor collection system.

Alternative configurations (as shown in FIG. 2) utilize a heat source located on the surface, outside of the well, with an energy conduction conduit to supply energy to the subsurface heating element. The energy conduction conduit could be a pipe or tube through which a heated ‘working fluid’ flows, or it could be a wire through which electric current flows, or it could be a fiber optic cable through which light energy is delivered to the heating element which converts the energy supplied to heat and radiates and/or conducts the heat to the soil or regolith in a region surrounding the well.

Alternate configurations (as shown in FIGS. 3 and 4) utilize curved or horizontal drill-holes to extract a distributed subsurface frozen volatile substance from regions that are not located directly below the well hole entrance. Multiple curved or horizontal drill holes could emanate from the same central well site where the collection, condensation, and storage units are located. Several nearly parallel horizontal drill holes could be utilized to create a sub-surface high horizontal permeability zone in a region containing a significant deposit of the frozen volatile substance, enhancing the ability to heat the soil and extract the volatile substance in that desirable extraction region.

As shown in FIG. 1 extraction well 101 has a well-bore or drill-hole 100 drilled into a regolith (or soil or other subsurface) deposit 110 containing a frozen volatile substance distributed within the regolith or soil. A self-contained heating element 125 is placed in the well at a depth where the volatile extraction is to take place. Heating element 125 may be self-actuating or actuated by a signal from the surface, e.g. on a cable or by radio, and may be on a track or cable so that it can move or be moved to different positions along the borehole. An extraction tube 142 is inserted into the well and extends upward therefrom, and a vapor-seal region 130 is established in the well hole, near the well entrance, to prevent vapor from escaping from the well. Heat 126 from the subsurface heating element 125 radiates and is conducted into the surrounding nearby volatile-containing regolith or soil 110, establishing a heated zone 140 in the subsurface region surrounding the heating element. As the frozen volatile substance in the regolith is heated, some of it is vaporized and the resulting increase in vapor pressure in the pores within the regolith will tend to drive the vapor 141 toward a low pressure region, i.e. the borehole 100. The surface-located condensor/collector 143 is connected to the well-bore hole 100 via the extraction tube 142 and condenses the arriving volatile vapor (extracted from the soil or regolith) and maintains a low pressure in the extraction tube 142. The low pressure in the extraction tube 142 and well bore hole 100, provide a preferred path along which the newly vaporized volatile substance 141 will migrate from heated zone 140 of regolith or soil 110. The volatile substance 141 collected by collector 143 is condensed and then passed through pipe 144 to a storage tank 146.

The effective thermal conductivity of regolith on airless bodies such as the moon is extremely low (e.g. the thermal conductivity of lunar regolith is on the order of ˜0.00015 W/cm K under in situ vacuum conditions), but that effective thermal conductivity increases by as much as a factor of 100 if an interstitial gas is present in the pore space in the regolith. The rate of transfer of heat from the heating element 125 to the surrounding regolith 110 will increase significantly if the effective conductivity increases. As the average temperature in the extraction region increases, the operating pressure in the well bore and extraction tube can be increased somewhat, and still remain at a value lower than the vapor pressure of the vaporizing volatile substance being extracted. Increasing the operating pressure in the well bore and the surrounding regolith interstitial space has the effect of increasing the effective thermal conductivity in the heated regolith, which allows heat to flow more readily through it, allowing the surrounding region to be heated more easily, subsequently allowing release of more volatile substance as vapor.

As shown in FIG. 2 an extraction well 201 for extraction of frozen subsurface volatile substances is similar to well 101 of FIG. 1 except that in this embodiment of the invention the subsurface heating element 225 is connected to a surface-mounted source of energy 223 via a conduit 224 through which that energy flows. The energy from the surface could be in any of several forms including light, sensible heat of a fluid, electric current, or any other form that can easily be transferred along a conduit or cable. For example, if the energy is delivered to the heating element as visible, infrared or ultraviolet light, then the conduit 224 could be a fiber optic cable and the heating element 225 could simply direct the light onto the regolith 210 surrounding the bore hole 200 where it would be absorbed by the soil, causing the temperature of the soil to rise. When sunlight 220 is available, as shown in FIG. 2, such light energy 220 could come from a remotely located solar collector/reflector 221 which directs the sunlight to a light receiver 222 on the surface-mounted energy-source 223. While sunlight is available the surface-mounted energy-source unit would direct the light into the fiber-optic cable/conduit 224 for transmission to the subsurface heating element 225. The surface-mounted energy source could also be constructed so as to convert a portion of the solar energy received into electrical energy so that it could readily be stored, in a battery for example, for utilization during times when the sunlight is not present. That stored energy could later be converted to light or electric current and sent to the subsurface heating element 225 during times when sunlight is not available. Extraction well 201 is otherwise similar to extraction well 101 of FIG. 1. Well-bore or drill-hole 200 is formed in regolith or soil deposit 210. After cable/conduit 224 and heater 225 are placed in the well 200, and extraction tube 242 is inserted thereinto, the top of well 200 is closed by a seal 230. Heat 226 from heater 225 then releases vapor 241 from heated zone 240. The vapor is collected through extraction tube 242 at collector/condenser 243 where it is condensed and passed through pipe 244 to storage tank 246.

In one embodiment of the invention, the surface mounted energy-source 223 could use a working-fluid or gas to transfer energy in the form of the sensible-heat of the working-fluid to the subsurface heating element 225, via the conduit 224. The energy to heat the working fluid could come from any number of sources, including but not limited to, radioactive materials, chemically stored energy, sunlight or other energy sources. In another embodiment of the invention, the energy-source 223 could be designed to generate or utilize electric current to transfer energy via an electrically conducting wire or cable 224 to a heating element 225 consisting of an electrical-resistance heating element or a microwave radiating heater. That electrical energy could be stored as chemical potential energy (e.g. in a battery), or it could originate from sunlight and be converted to electrical energy via photovoltaic cells. In such an embodiment the light-receiver 222 indicated in FIG. 2 could be a set of photovoltaic (PV) cells to convert light 220 received from a solar collector/reflector 221 to electrical energy or solar collector 221 could be a PV array.

FIG. 3 shows a well 301 for extraction of frozen subsurface volatile substances similar to the well 201 of FIG. 2, except that the well borehole 300 is curved so that the extraction region 340 is not located directly beneath the well entrance or the collection/condensation unit 343. FIG. 3 shows the heating element 325 and the extraction region 340 of the well bore hole 300 in an essentially horizontal orientation; however, a curved bore hole 300 could also lead to a similar configuration which is inclined at any angle between horizontal and vertical. The physical process for radiating and conducting heat 326 from the heating element 325 into the surrounding soil 310 to form a heated region 340, and the subsequent counter flow of the vaporized volatile substance 341 toward the well borehole and on out through the collection tube 342 to the collection unit 343 is the same as described for vertically oriented extraction regions and shown in FIGS. 1 and 2. The seal at the top of borehole 300 is not shown. As shown sunlight 320 is collected by collector/reflector 321 and directed to light receiver 322 on surface mounted energy source 323, which provides energy to heater 325 through conduit or cable 324. Heater 325 produces heat 326 to heat zone 340. The collected vapor is condensed in condenser 343 and passed through pipe 344 to storage tank 346.

FIG. 4 shows an embodiment of the invention similar to FIG. 3 except that the curved and horizontal portions of the well 401 consist of a manifold of nearly parallel boreholes 402 emanating from the same vertical entrance hole 400. In FIG. 4 the down-hole portion of a heat-carrying conduit 424 is shown as a single dashed line that branches into several separate conduits 428, with one conduit inside of each of the nearly parallel boreholes 402. A set of heating elements 425 is located in the extraction region with one heating element for each of the nearly parallel boreholes 402. The entire set of heating elements 425 serve to heat an extraction region 440 that has a larger extent in directions perpendicular to the borehole 400 than would occur from just a single borehole. Such a configuration would be particularly useful for extracting volatile substances from a subsurface deposit 410 that has a relatively large horizontal extent or range, but only occupies a relatively small vertical depth range. Such a configuration could also facilitate the creation of a horizontal region of high permeability by pressurizing successive sections of multiple adjacent boreholes to briefly raise the overburden material a small amount. A temporary vertical expansion of a small horizontal region would create a permanent increase in the horizontal permeability below that lifted region. This high permeability region could then form a high production region for extraction of volatiles since both heat and vapor flow would be increased in that region. The surface energy generation system formed of elements 421, 422, 423 powered by sunlight 420 is similar to those shown in FIGS. 2 and 3, as are extraction tube 442, condenser 443, pipe 444, and storage tank 446. The seal at the top of borehole 400 is not shown. In an alternate embodiment, the multiple horizontal boreholes 402 do not have to be nearly parallel but can be at larger angles to each other to cover a wider zone around the vertical borehole 400.

Additional alternate configurations could also be implemented. For example, the extraction wells could be configured to have a ‘low point’ where liquid water would collect, with a slightly upward sloping collection ‘well’ hole continuing beyond the low ‘collection’ point. Liquid water could be pumped from the low-point to a surface collection vessel; however, pumping liquid is likely to be much more problematic than transporting vapor, so configurations that rely on simple pressure differences and maintain the desired volatile component in its vapor-state are likely to be more robust configurations for most anticipated volatile extraction operations and are thus usually preferred embodiments of the invention. An optimal configuration for these extraction wells will depend on the prevailing temperature in the regolith deposit, and how much added heat is required to maintain the system in a desired operating temperature range.

The method of this invention does not involve mining and extracting regolith before removing the frozen volatiles; thus it uses less energy, and is less costly than approaches that require mining of regolith as proposed by Zacny et al. The approach does not involve construction of a gas-tight pressurized dome over the region of regolith to be processed, and so is less costly than alternative methods proposed for utilizing solar heat for insitu extraction of volatiles as proposed by Wittenberg. The only drilling or mining required for establishing the volatile extraction-well collection/recovery system is a well-bore drill hole, which may include vertical, inclined or curved and horizontal or upsloping extraction-well ‘drill-holes’. In its simplest form the volatile extraction wells will function without pumps, compressors or other down-hole gas-moving equipment, relying instead on conduction and radiation for thermal transport into the soil and diffusive vapor transport and thermally induced convection of the vaporized volatiles for transport of the released vapor to the collection location(s). These volatile extraction wells could represent a significant advance in extraction efficiency for recovery of frozen volatiles in subsurface deposits on the Moon, Mars, or other extraterrestrial bodies.

Although the description above contains many details, these should not be construed as limiting the scope of the invention but as merely providing illustrations of some of the presently preferred embodiments of this invention. Therefore, it will be appreciated that the scope of the present invention fully encompasses other embodiments which may become obvious to those skilled in the art, and that the scope of the present invention is accordingly to be limited by nothing other than the appended claims, in which reference to an element in the singular is not intended to mean “one and only one” unless explicitly so stated, but rather “one or more.” All structural and functional equivalents to the elements of the above-described preferred embodiment that are known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the present claims. Moreover, it is not necessary for a device to address each and every problem sought to be solved by the present invention, for it to be encompassed by the present claims. Furthermore, no element or component in the present disclosure is intended to be dedicated to the public regardless of whether the element or component is explicitly recited in the claims. No claim element herein is to be construed under the provisions of 35 U.S.C. 112, sixth paragraph, unless the element is expressly recited using the phrase “means for.” 

1. A volatile extraction well for extracting a frozen subsurface volatile substance from soil or regolith, comprising: a borehole drilled into the soil or regolith; a heating element inserted in the borehole at a depth where the volatile substance is to be extracted and capable of radiating or conducting sufficient thermal energy to the soil or regolith to vaporize the frozen volatile substance; a gas seal formed at or near the top of the borehole to prevent uncontrolled escape of vapor from the borehole when released by the heating element; an extraction tube or conduit extending through the gas seal for removing vapor from the borehole when released by the heating element.
 2. The well of claim 1 wherein the borehole is substantially vertical or tilted at an angle to the vertical.
 3. The well of claim 1 wherein the borehole is curved.
 4. The well of claim 3 further comprising a plurality of substantially horizontal boreholes extending from the bottom of the curved borehole.
 5. The well of claim 1 wherein the heating element is self-contained within the borehole.
 6. The well of claim 1 further comprising a surface mounted energy source and a conduit or cable extending through the gas seal to the heating element to connect the heating element to the surface mounted energy source.
 7. The well of claim 6 wherein the surface mounted energy source is solar powered.
 8. The well of claim 1 further comprising a surface located collector and condensor connected to the borehole through the extraction tube or conduit for collecting and condensing vapor from the borehole when released by the heating element.
 9. The well of claim 8 wherein the collector and condensor maintains a sufficiently low pressure in the borehole to allow vapor released by the heating element to flow to the collector and condensor.
 10. The well of claim 9 wherein the collector and condensor maintains the pressure in the borehole below the boiling pressure of the volatile substance being recovered, corresponding to the temperature of the heated subsurface region of the well.
 11. A method for extracting a frozen subsurface volatile substance from soil or regolith, comprising: drilling a borehole into the soil or regolith; inserting a heating element in the borehole at a depth where the volatile substance is to be extracted, the heating element being capable of radiating or conducting sufficient thermal energy to the soil or regolith to vaporize the frozen volatile substance; forming a gas seal at or near the top of the borehole to prevent uncontrolled escape of vapor from the borehole when released by the heating element; providing an extraction tube or conduit extending through the gas seal for removing vapor from the borehole when released by the heating element.
 12. The method of claim 11 wherein the borehole is substantially vertical or tilted at an angle to the vertical.
 13. The method of claim 11 wherein the borehole is curved.
 14. The method of claim 13 further comprising providing a plurality of substantially horizontal boreholes extending from the bottom of the curved borehole.
 15. The method of claim 11 wherein the heating element is self-contained within the borehole.
 16. The method of claim 11 further comprising providing a surface mounted energy source and a conduit or cable extending through the gas seal to the heating element to connect the heating element to the surface mounted energy source.
 17. The method of claim 16 wherein the surface mounted energy source is solar powered.
 18. The method of claim 11 further comprising providing a surface located collector and condensor connected to the borehole through the extraction tube or conduit for collecting and condensing vapor from the borehole when released by the heating element.
 19. The method of claim 18 wherein the collector and condensor maintains a sufficiently low pressure in the borehole to allow vapor released by the heating element to flow to the collector and condensor.
 20. The method of claim 19 wherein the collector and condensor maintains the pressure in the borehole below the boiling pressure of the volatile substance being recovered, corresponding with the temperature of the heated subsurface region of the well. 